A. Field of the Invention
The present invention generally relates to vacuum cleaners and, more particularly, to a vacuum cleaner constructed to prevent the accumulation of a high level electrostatic charge on its components.
B. Description of the Prior Art
As a general principle, any two dissimilar bodies coming into frictional contact will generate an electrostatic charge. An electrostatic charge may accumulate on components of a vacuum cleaner due to this principle and to the flow of particulate matter passing through the vacuum cleaner. In extreme situations, the accumulated electrostatic charge may reach an electrical potential sufficiently high to cause an electrostatic discharge, risking an unpleasant or harmful shock to the user of the vacuum cleaner or damage to the electrical controls of the vacuum cleaner. Furthermore, the accumulated charge may result in a build up of particulate matter on the inner surfaces of the vacuum cleaner components that, in some cases, may interfere with material movement through the vacuum cleaner.
Several efforts have been made in the past to eliminate or control the accumulation of electrostatic charge. One suggested effort involved the use of antistatic material in the fabrication of the components of an implement as discussed in U.S. Pat. No. 2,108,759. The use of antistatic materials has the disadvantage of significantly increasing the cost of the implement. Another prior art approach disclosed in U.S. Pat. No. 390,196 involved electrically connecting all the conductive components of an implement and directing a spark discharge to an area of little danger to the implement or the implement user. A significant problem with using that approach on a household implement such as a vacuum cleaner is that the possibility of shock to the user is not necessarily eliminated.
Another proposed solution disclosed in U.S. Pat. No. 1,920,889 is to dissipate the electrostatic charge through the body of the user of an implement. This proposal also has the significant disadvantage of user shock and would be unacceptable for use in vacuum cleaners.
It is desirable in the vacuum cleaner art to maintain the level of the electrical potential due to electrostatic charge accumulation to a level below the threshold for shock sensation detectable by a user, i.e., below the range of approximately 5,000 to 10,000 volts.